The mother starts the weaning process about four weeks after birth. She makes suckling more difficult. She does this by
- avoiding her kittens and;
- adopting body postures which makes her nipples less accessible.
This process takes place over about three weeks. At seven weeks of age suckling is at a low level. The kittens obtain most of their nutrition from solid food. At this point weaning has finished. Although occasional suckling without milk may occur for several months particularly if there is sole kitten.
Below is a cute short video of a mother and her kittens who scram when she misses her jump:
Weaning is an unaggressive process unless and perhaps if food supplies are poor. Some experts believe that mothers curtail weaning if the food supply is poor. Alternatively some experts believe that weaning will be extended under these circumstances to ensure the kittens are ready to be independent. The former theory favours the mother’s survival to allow her to raise young again while the latter favours the current offsprings’ survival.
Source: The Domestic Cat: The Biology of its behaviour.